Cathode ray tube



F. VAN HEKKEN Dec. 27, 1966 CATHODE RAY TUBE Filed Aug. 6. 1962 2Sheets-Sheet l INVENTOR. f/m/.s mv /v/f/EA/ BYl g Arran/fr F. VAN HEKKENCATHODE RAY TUBE Dec. 27, 1966 2 Sheets-Sheet 2 Filed Aug. e, 1962 e 4uFan/5 M ,6M/65 aff/v INVENTOR.

. WL/Zm fyi@ /1 Trai/Vif United States Patent O 3,294,999 CATHODE RAYTUBE Frans van Hekken, East Lampeter Township, Lancaster County, Pa.,assignor to Radio Corporation of America, a corporation of DelawareFiled Aug. 6, 1962, Ser. No. 215,011 17 Claims. (Cl. 313-70) Thisinvention relates to cathode ray tubes of the type -utilizingdifferential penetration of a luminescent screen by a plurality ofdifferent velocity electron beams to vobtain plural color imageproduction.

One type of cathode ray tube referred to above includes a luminescentscreen having three different phosphors which are disposed insuperimposed layers, each of which is capable of emitting, for example,a different one of the three primary colors, red, green, and blue. Thetube further includes three electron guns, each adapted to project adifferent velocity electron beam through a common deflection field andonto the luminescent screen. Electrons of the lowest velocity 4beamexcite the first phosphor layer to produce light of a first color;electrons o f the medium velocity beam penetrate the first layer andexcite the second layer to produce light of a second color; andelectrons of the highest velocity beam penetratejboth the first andsecond layers and excite the third layer to produce light of a thirdcolor. Proper current vintensity modulation of the three beams enablesproduc- -tion of any desired mixture of these three colors.

In tubes of the type described if an assembly of prior art electron gunsof a type suitable to give the desired performance is used, at leastfifteen separate lead-in conductors in addition to a high voltage ultorterminal are required. If Iall fifteen lead-ins are brought into thevacuum enclosure through a standard stem structure, the greatlydifferent voltages on the conductors often cause voltage breakdown atthe stem, the base, or the socket. The available alternative of bringingin some of the leadins through the vacuum enclosure at other places thanthe stem is costly and otherwise undesirable because of the diiculty ofsocketing the terminals of these lead-ins, and also because of theirphysical interference with various tube adjuncts. Even a slightreduction in the number of required lead-ins can result in a significantincrease in spacing between lead-ins at the stem and in a consequentsignicant increase in the resistance to voltage breakdown therebetween.

It is therefore an object of this invention to provide a new andimproved plural gun cathode ray tube of the type described whichrequires fewer lead-in conductors than that required by prior art tubes.

The invention is embodied in a cathode ray tube having a luminescentscreen and a plurality of electron guns, each of which is adapted toproject a different velocity electron beam. Each of the guns comprisesat least a cathode, a control electr-ode, and an electrostatic focuslens system.

According to one feature of the invention, one set of correspondingelectrodes of the lens systems of all the guns are interconnected andenergized with a common focus voltage so as to reduce the requirednumber of leadins. In order to compensate for the unequal effect of acommon focus voltage on three different velocity electron beams, thelens systems are so relatively constructed and positioned that they al1focus their respective beams structed and/ or positioned that thetransfer characteristicsl of the guns are made to conform -to a desiredrelationship (e.g., made equal) when the guns are differentiallyenergized to produce the different velocity electron beams.

In the drawings:

FIG. 1 is a side elevation view, partly in section and with parts brokenaway of a cathode ray tube embodying lthe invention;

FIGS. 2, 3, and 4 are transverse sections of the cathode ray tube ofFIG. 1 taken respectively along lines 2 2, 3--3, and 4 4;

FIG. 5 is a semischematic illustration of the electron gun assembly ofthe tube Iof FIG. 1;

FIGS. 6 and 7` are semischematic illustrations of differentmodifications of the electron gun assembly of the tube of FIG. l; and

FIG. 8 is a plan View of an electron gun stem suitable for use withelectron gun assemblies of FIGS. 5,. 6, and 7.

General tube description FIGS. l, 2, 3, 4, and 5 illustrate a cathoderay tube 8 comprising an evacuated envelope including a neck section 10,a faceplate 12, and an interconnecting lfunnel section 14. Disposedwithin the neck 10 is an electron gun assembly 15 comprising, forexample, three electron guns 16, 17, and 18 positioned side-by-side `inla delta triangular array and each attached at one end to a convergence-cage 19, hereinafter described. In FIG. l, gun 17 is hidden behind gun16. The electron guns 16, 17, and 18 are respectively adapted to projectlower, medium, and higher velocity electron beams -through a commondeflection zone 20 and toward the faceplate 12. For the purpose ofbrevity and clarity, the terms L beam, M beam, and H beam will behereinafter used to refer respectively to the lowest velocity beam (andits gun 16), the medium velocity beam (and its gun 17), and the highestvelocity lbeam (and its gun 18).

A luminescent screen 21 on the faceplate 12 includes three layers 22,24, and 26 of different phosphors, each of which luminesces in adifferent one of the three primary colors, blue, green, and red. In thedrawings the phosphor layers 22, 24, and 26 `are shown as continuousover the entire faceplate 12. However, the layers may be provided inother suitable forms su-ch as a multiplicity of particles each of whichincludes superimposed coatings of the different phosphors.

The tube 8 is operated so that electrons of the L beam will excite thefirst phosphor layer 26 to produce light of a first primary color;electrons of the M beam will penetrate the first phosphor layer 26 andexcite the second phosphor layer 24 to produce light of a second primarycolor; and electrons of the H beam will penetrate both the first andsecond phosphor layers 26 and 24 and excite the thi-rd phosphor layer 22to produce light of la third primary color. A metal Ibacking layer 27of, e.g., aluminum, is disposed over the phosphor layer 26 as is knownin the art. If desired, the screen 21 may include non- Pafented Dec. 27,196ey luminescent separator layers between the phosphor layers toimprove the operational characteristics of the screen.

A plurality of spring snubbers 30 are fixed to the convergence cage 19and bear outwardly against the neck 10 of the envelope. The snubbers 30serve both to support one end of the electron gun assembly in the neck10 and to make electrical contact with a conductive coating 32 on theinternal surfa-ce of the envelope. The coating 32 extends over thefunnel 14 into electrical contact with the metal backing layer 27 of theluminescent screen 21, and into the neck a suicient distance to makecontact with the snubbers 30. Terminal means, such as is illustratedschematically by the arrow 34, is provided for applying a suitable ultorelectrical potential to the coating ele-ctrode 32 and the other tubeparts electrically connected thereto.

The end of the electron gun assembly 15 opposite the convergence cageend is, for example, supported on some of a plurality of stiff terminalpins 36 which are sealed through the vacuum envelope of the tube in astem structure 38 (FIG. 8). The electrodes of the electron guns, otherthan those connected to the ultor potential through the terminal 34, areenergized through the pins 36.

Electron gzm assembly As shown in FIGS. l and 2, the three electron guns16, 17, and 18 are preferably disposed in delta array. Such an arrayprovides an electron gun assembly which is both compact and compatiblewith known electron beam convergence techniques. However, the electronguns may be in either linear or triangular array. For the purpose ofmore clearly illustrating the invention, electron guns 16, 17, and 18 ofthe delta assembly 15 of FIG. 1 are shown in FIG. 5 as spread outside-by-side in linear array.

, Each of the electron guns 16, 17, and 18 includes a cathode 4t), acentrally apertured cup-shaped control electrode 42, and a heaterlilament 44 disposed within the cathode. The cathode, control electrode,and heater filament for each of the electron guns are preferably similarto that of the others. Each of the electron guns includes anelectrostatic focus lens system, preferably a unipotenrtial(Einzel-type) lens system, as dened on page 96 by I. G. Malotf and D. W.Epstein in Electron Optics in Television, published by McGraw-Hill BookCompany, Inc., New York, 1938. The lens system of each gun differs fromthat of the others by virtue of the dimensions and/or spacings of theelectrodes thereof. The lens systems of the three guns 16, 17, and 18respectively, cornprise tubular first anodes 46, 47, and 48, tubularsecond anodes 50, 51, and 52, and tubular focus ring electrodes 54, 55,and 56. The first and second anodes of each gun are axially spaced toprovide a gap therebetween. The focus ring of each gun is of largerdiameter than the adjacent ends of the associated pair of anodes of thegun and is disposed surrounding the gap between the anodes with its endsslightly overlapping the adjacent ends of the anodes.

The electrodes (other than cathode) of each of the electron guns 16, 17,and 18 are maintained in xed, spaced, coaxial relationship in awell-known manner such as by mounting them on three glass rods 58 whichextend along the guns. The electrodes of each of the three guns arefixed to the glass rods by metal straps 60. Each strap has an arcuatecenter section (FIG. 2) mating with its electrode and end portions whichare embedded into two of the glass rods 5S. One of the straps 60, e.g.,the one on the first anode 48 of the H gun 18 may be made of magneticmaterial for a purpose hereinafter described. Further details of themounting of the electron guns 16, 17, and 18, which are conventional,have been omitted from the drawing for purposes of clarity.

The second anodes 50, 51, and 52 of the three guns are mounted on theelectrically conductive convergence cage 19 and are thus allelectrically common with each other and with the convergence cage. Theconvergence cage 19 comprises a cylindrical cup which has an end wall 62and which is closed at its open end with an end plate 63 (FIG. l). Boththe end wall 62 and the end plate 63 are provided with three apertures64, 65, and 66. The pair of apertures 64 are coaxially aligned with theelectron gun 16, the apertures 65 with the gun 17, and the apertures 66with the gun 1S (FIGS. 3 and 4).

As is shown in FIG. 5, the first and second anodes of the three electronguns are all electrically interconnected. The three second anodes 50,51, and 52 are all electrically common, being connected to theconvergence cage 19. The three first anodes 46, 47, and 48 are connectedtogether and to the three second anodes and convergence cage by internalconductors represented at 68, 69, and 76.

In operation of the electron gun assembly 15 of FIGS. 1-5, an ultorpotential of, for example, +19 kilovolts is applied to the convergencecage 19 and the six anodes via lead 72 (FIG. 5). As shown in FIG. 1,this voltage application is made through the voltage terminal 34, theconductive envelope coating 32, and the snubbers 30. Each one of thecathodes 40 of the three guns 16, 17, and 18 is operated at a potentialdifferent from the other cathodes so as to provide three differentvelocity electron beams. For example, the cathode of the H gun 18 isoperated at -7 kilovolts, the cathode of the M gun 17 at O volts, andthe cathode of the L gun 16 at +6 kilovolts. Electron beams of 26kilovolts, 19 kilovolts, and 13 kilovolts are thus provided by the Hgun, M gun, and L gun, respectively.

Because the lvelocities of all the beams are different, at least oneparameter determining the transverse surface at which the beams arefocused must be different for each beam. I have found that all the`beams can be focused at a common image surface without resorting todifferential energization of the focus lenses. Instead, the focus lenssystems of the guns are so differentially arranged that the lenseseither are of different strength or are staggered along the tube axis toposition them different distances from the common image surface or both.For example, in the electron gun assembly 15 of FIGS. 1 5, differentstrength electrostatic unipotential focus lenses are provided to focusthe beams at a common image surface. Thus the number of lead-inconductors through the vacuum enclosure of the tube, as well as thenumber of different voltages used, is reduced over those used in priorart tubes.

As shown in FIG. 5, the three focus rings 54, 55, and 56 areelectrically connected together by conductors 74 and 76, and a singleconductor 78 is connected between the focus rings and one of the pins 36(FIG. l) of the stem 38. If desired, the focus rings 54, 55, 56 maydirectly contact each other and the conductors 74 and 76 may be omitted.The spacing between the first and second anodes of each gun is madedifferent from that of each of the other guns, so that the common focusvoltage applied via conductor 7 3 provides three different strengthfocus lenses. The spacing between the anodes of each gun is directly(but not necessarily linearly) related to the velocity of the electronbeam of that gun so as to provide the proper strength of lens for eachbeam. Specifically, the anodes 48 and 52 of the H gun, which has thehighest beam velocity, are spaced the farthest apart. The anodes of theM gun are spaced closer together than those of the H gun, and the anodesof the L gun still closer.

The greater or lesser spacing between the anodes of each of the gunsresults in the electrostatic eld from the focus ring electrodespenetrating a greater or lesser distance into the gaps between theanodes. The greater this field penetration (for a given differencebetween the voltages on focus ring and anodes of a gun), the strongerthe lens will be. Such greater penetration, and hence lens strength, canalso be obtained as shown in FIG. 6.

FIG. 6 illustrates a modification of the electron gun assembly of FIGS.1-5. The electron gun assembly of FIG. 6 is si-milar to the assembly 15except for the separate focus lens systems for the three guns. In FIG..6 the H gun lens system comprises two spaced anodes 80, 81 and anapertured disk focus ring 82 which surrounds a portion of the gapbetween the anodes. Similarly, the M gun lens system comprises a pair ofspaced anodes 83, 84 and a disk focus ring 85, Vand the L gun comprisesanodes 86, 87 and focus ring 88. The six anodes and the convergence cage19 are electrically connected together by conductors represented at 89,90, 91. The three focusrings are electrically connected together byconductors 92 and 93. The anodes are energized through the conductor 94and the convergence cage 19; the focus rings are energized throughconductor 95.

In order to provide dierential penetration of the electrostatic fieldfrom :the focus rings into each of the gaps between the anodes of eachgun, the sizes of the apertures (internal diameters) of the focus ringsare made different from each other. The H gun, whose focus ring 82 hasthe smallest aperture, accordingly has the strongest focus lens. Thefocus rings of .the M and L guns have progressively larger apertures.The sizes of the focus ring apertures are so related to the velocitiesof ythe respective beams that the beams are Ifocused to a small spot atthe common image surface, or luminescent screen.

If desired, the three separate focus rings 82, 85, 88 may be provided asa single plate with three separate apertures of the different desiredsizes properly positioned to be disposed coaxially with their respectiveguns.

The lens arrangements of both FIG. 5 and FIG. 6 have the common featureof providing separate lenses for the three guns which are of differentstrength. In the embodiments of both FIGS. 5 and 6 the ratio of spacinglbetween the anodes of each gun to the internal diameter of its focusring is different from that of the other guns.

In electron guns having unipotential-type lenses, a screen gridelectrode (usually in the form of a centrally apertured cup-shapedelement) is conventionally provided between the control electrode andthe lens system of the gun. In the electron guns of either the FIG. 5 orFIG. 6 embodiments, such screen electrodes are omitted to further reducethe number of lead-in conductors required to operate the tube. In theseembodiments, which are void of screen grid electrodes, the controlelectrode 42 and the rst anode electrode -(e.g., 48) of each gun arenext adjacent =to each other. That is, there is no electrode interposedbetween the control and iirst anode electrodes.

Without a screen grid electrode the potential difference between thecathode and the nearest anode (the electrode next adjacent the controlelectrode) is different for each of the three guns since the cathodesare operated at different potentials. If no allowance is made for thisdifference, the electron acceleration voltage gradient at the cathode,due to Ithe anode electrostatic field dipping into and through theaperture in the control electrode, will result in the three electronguns having substantially different transfer characteristics.Specifically the slopes of the drive characteristics (gammas) and thebeam cutolf voltages of the three guns may be quite different. Transfercharacteristics :may be defined as the relation Ibetween .the voltageinput on one electrode (e.g., the control electrode) and the output(current or light) from another electrode (e.g., the luminescentscreen), all other electrode voltages being :maintained constant.

Usually it is desired that the transfer characteristics of all the gunsbe substantially equal. However, in some applications it may be desiredto make the transfer characteristics of the guns conform to somepredetermined relationship wherein they are not exactly equal. Forexample, it may be desired to make them unequal by predetermined amountsso as to compensate for nonuniformity of the responses of the differentphosphors of the screen.

In order to obtain a predetermined relationship of the transfercharacteristics of the three guns, the dimensional and/or spacingrelationship-s Ibetween the cathode, control electrode and next adjacentanode (first accelerating) electrode are preselected. For example,substantially equal transfer characteristics can be obtained by makingone or more of these dimensional or spacing relationships different foreach gun. Specifically, one or more of the following parameters may bemade different for each gun: (l) the spacing between control electrodeand the next adjacent anode, (2) the spacing between cathode and controlelectrode, and (3) :the control electrode aperture diameter. For a givenpotential difference between cathode and the nearest anode electrode: acloser spacing between control electrode and next .adjacent anoderesults in a lower overall gamma and higher cut--otf voltage, a closerspacing tbetween cathode and control electrode results in a loweroverall gamma and higher cut-off voltage, and a smaller controlelectrode aperture diameter results in a higher gamma and lower cut-oitvoltage.

As an example, substantially equal transfer characteristics of the threeguns are obtained in the embodiments of FIGS. 5 and 6 by making thespacing between the control electrode and the first anode of each of theelectron guns different from that of the other guns. Since in the H gun18 (FIG. 5) the voltage difference between the first anode 48 and thecontrol electrode 42 is greater than that between correspondingelectrodes of the other guns, the spacing between its rst anode andcontrol electrode is made greater than that of the other guns. Thespacings between the first anodes and control electrodes of the M and Lguns are related to the voltage differences between their controlelectrodes and first anodes and are therefore correspondingly less thanthe spacing between .these electrodes of the H gun.

In the embodiments of FIGS. 5 and 6 an electron gun which has a strongerfocus lens than does another gun is designed to have (with identicalvoltages applied to corresponding electrodes) a higher gamma.Specifically', the gun which has a greater spacing between its twoanodes than does another of the guns (stronger focus lens) has a greaterspacing `between its first anodeand control electrode than does the saidanother of the guns, to produce the desired higher gamma. For example,in FIG. 5, the H gun which has the greatest spacing between its twoanodes, also has the greatest spacing between its control electrode andfirst anode. Each of these corresponding spacings in the M and L guns isrespectively progressively less.

As is known in the art, the cathode of an electron tube may beinternally connected to one of the heater filament leads. If thisexpedient is used in the electron gun assembly 15 0f FIGS. 1-5, thetotal number of lead-in conductors in excess of the ultor terminal 34 isreduced to ten. In an otherwise comparable tube not employing thisinvention, as high as fifteen lead-in conductors might be required.

If desired, the lengths of the electrodes of all three electron guns 16,17, and 18 may be identical and the spacing between the controlelectrode and lirst anode and the spacing between the rst anode andsecond anode be different for the three guns. However, it is preferredto make all three electron guns the same overall length for mechanicalpurposes. Accordingly, it is preferred to compensate for `thedifferential spacing between electrodes of the guns by making the firstanodes 46, 47, and 48 of different lengths as best shown in FIG. 5. Ifdesired, one or more of the focus rings 54 and 55 may be of shorterlength than that required for the focus ring 56 of the H gun. In FIG. 5the focus rings 54 and 55 of the L and M guns are shown equal in lengthand shorter than the focus ring 56 of the H gun.

DIMENSIONS H gun 18, M gun 17, L gun 16, mils mils mils 1st anode-2danode spacing 475 350 250 1st anode-control electrode spacing 310 265210 Cathode, control electrode spacing 10 10 1st anode, 2d anode,control electrode diameter 375 375 375 Focus ring diamete 500 500 500Focus ring length 625 500 500 1st anode length 555 715 880 Controlelectrode aperture diameter 25 25 25 1st anode lower aperture diamer 7575 75 1st anode upper aperture diameter 175 175 175 2d anode aperturediameter 175 175 175 VOLTAGES H gun 18 M gun 17 L gun 16 Cathode -7kv..-" O volts +6 kv. Control electrode 7,100 to -100 to +5,900 to 7,150v. -150 v. +5,850 v Focus ring (all three the samc) +300 v +300 v +300v. 1st and 2d anodes, convergence +19 kv +19 kv +19 kv cage andluminescent screen.

FIG. 7 illustrates a modication of the electron gun -assembly of FIGS.1-5 in which centrally apertured, cup-shaped screen electrodes 100, 101,and 102 are provided respectively, for the L gun, M gun, and H gun. Inthe electron gun assembly of FIG. 7, the practice of differentialspacings between the first anodes 103, 104, 105 and second anodes 106,107, 108 of the three guns is used as hereinbefore described withreference to FIG. 5. As shown in FIG. 7, both the first anodes 103, 104,105 and second anodes 106, 107, 108 may be made of different length fromgun to gun so as to provide equal overall lengths of the three guns.Specifically, the spacing between the anodes 104 and 107 of the M gunmay be made greater than the spacing between the anodes 103 and 106 ofthe L gun and less than the spacing of the anodes 105 and 108 of the Hgun by making the anodes of the M gun, respectively, shorter than theanodes of the L gun and longer than the anodes of the H gun.

Like the electron gun assembly 15 of FIGS. l-5, the gun assembly of FIG.7 has its three focus rings 109, 110, 111 connected together andenergized by a common focus potential through conductor 112. Even withthe addition of the screen electrodes 100, 101, 102, the electron gunassembly of FIG. 7 requires not more than thirteen lead-in conductors inaddition to the ultor terminal 34.

The voltages set forth above, for the operation of the e-lectron gunassembly 15 of FIG. 5 may, for example, be applied to correspondingelectrodes of the electron gun assembly of FIG. 7. Each of the screenelectrodes 100, 101, 102 of the electron gun of FIG. 7 may be suitablyenergized respectively, with a potential of approximately 300 voltspositive with respect to the cathode of the same gun.

FIG. 8 illustrates one design of standard stem structure suitable foruse with the cathode ray tube 8 of FIGS. 1-5. The stem 38 of FIG. 8comprises a circular insulator wafer 114 having a centrally disposedexhaust tabulation 115 and a circular array of fourteen fillets 116formed integrally with the wafer 114 as thickened portions thereof. Tenpins 36 are sealed through selected ones of the fillets 116 as shown inthe figure. It is preferred that the ten pins 36 be separated intoeither three groups or four groups as shown in the figure. The lead 78(FIG. 5) from the focus rings 54, 55, 56 is connected to one of the pins36 which may either be grouped together with the cathode, heater, andcontrol electrode of the M gun, or preferably disposed alone with unusedfillets on either side thereof, as shown in the figure. Such groupingresults in an extra spacing between the pins having relatively largevoltage differences between them.

Auxiliary tube structure and adjuncts As an adjunct to the electron tube8, a magnetic deflection yoke 118 of known design is provided whichclosely encircles the envelope of the tube. The yoke 118, when suitablyenergized, is adapted to create horizontal and vertical magneticdeflection elds in the deflection zone 20 to cause the three separatebeams of the electron guns 16, 17, and 18 to scan a desired raster orpattern on the luminescent screen 21. A shield 120 may be provided atthe rear of the yoke 118 to reduce the rearward extent of the fringeportion of the deflection fields formed by the yoke.

Because the three electron guns 16, 17, and 18 are noncoaxial withrespect to the tube 8, each gun being mounted slightly off thelongitudinal axis of the tube, both static and dynamic convergence ofthe three beams is provided to compensate for this off axis mounting.Such convergence may be in accordance with known color televisionreceiver techniques.

Dynamic convergence may be provided as shown in FIG. 3. Two separatepole pieces 122 are disposed on opposite sides of each beam within theconvergence cagey 19. The pole pieces 122 are axially spaced back fromthe end plate 63 to reduce interference by the fringe of the deflectionfields with the field formed between the pole pieces 122.

Associated with each pair of pole pieces 122 is a separate electromagnet124 disposed externally of the tube envelope adjacent to the ends of thepole pieces. More refined arrangements, such as those incorporating apair of electromagnetic windings in place of the single winding 124, areknown in the art but for the sake of brevity and clarity are not hereindetailed. A Y-shaped magnetic shield 126 may be disposed within theconvergence cage for shielding each beam from the convergence elds ofthe other beams. l

Energization of the coils of the electromagnets 124 will individuallyimpart to its corresponding electron beam a small radial directionalcomponent of deflection toward or away from the longitudinal axis of thetube 8. A varying current synchronized with, and related to, the amount-of scanning deection of each of the three beams is separately appliedto each electromagnet 124 to provide the desired dynamic convergence ofthe three beams.

All three electron beams may be brought to a precise static convergenceat the center of the luminescent screen 21 by the combination of: (a) aslight mechanical convergence of the three guns 16, 17, and 18, (b)magnetic field means for adjusting the lateral position of one of theelectron beams, and (c) a static radial position adjustment of all threebeams through use of the electromagnets 124. The single beam lateraladjustment is accomplished by a magnetic field established in the pathof the H beam by a permanent magnet assembly 128. In order to help shapethe field of the magnet assembly 128 in the path of the H beam, themounting strap 60 on the first anode 48 of the H gun 18 may in someinstances be made of magnetic material. The field pro duced by themagnet assembly 128 is transverse to the `direction of the magneticfield established between the pole pieces 122 for the H beam. Thispermits -a lateral adjustment of the position of one of the threeelectron beams (viz., the H beam) in a direction which is normal to theradial adjustment of this same beam as provided by the convergence polepieces 122.

If desired, the poles of the magnet assembly may be dynamicallyenergized to provide an additional means contributing to the shaping ofthe H beam raster for the 9 purpose of registering this raster with therasters of the L and M beams.

Two thin-plate permanent ring magnets 130 and 132 are disposed aroundthe tube neck 10 behind the magnet assembly 128. The ring magnets 130and 132 are individually rotatable relative to each other to provide adesired intensity magnetic field transversely of the neck 10. Thismagnetic field serves to laterally position the three beams as a unit sothat they have an optimum relationship with the deflection fields in thedeflection zone 20.

Because of the different velocities of the three electron beams, ifpreventive or corrective measures were not taken, the beams would bedeilected different amounts by the common deilection fields of the yoke118. In order to obtain substantially equal deflection of the threebeams, the L gun 16 and M gun 17 are provided with-or have associatedtherewith-tubular magnetic shield members (i.e., magnetic shunts) 134and 136, respectively. Each of the shunts 134 and 136 may, eg., compriseeither a single tubular member of magnetic material or a plurality ofspaced coaxial rings of magnetic material mounted on a support. Theshields 134 and 136 are disposed coaxially with their respective guns 16and 17. The tubular shields 134 and 136 extend from, and are sopositioned with respect to, the electron gun apparatus that they aredisposed within the deflection zone 20.

The L beam shield 134 comprises -a plurality of, eg., five, rings 138 ofmagnetic material which are axially spaced from each other. The rings138 are mounted on a tubular support 140 of nonmagnetic material andlare thus maintained in the desired mutually spaced relationship. Thesupport 140 is fixed to the end plate 63.

The M beam shield 136 comprises a single tubular member 142 of magneticmaterial which is mounted axially spaced from the end plate 63 on anonmagnetic tubular support 144 which is fixed to the' end plate 63.

The cumulative axial length of the magnetic rings 138 of the L beamshield 134 is greater than the length of the magnetic tubular member 142of the M beam shield 136.

By virtue of the different cumulative shielding lengths of the shields134 and 136 and their disposition in the deflection zone 2f), the L andM beams are shielded from the detlection field over different portionsof their travel therethrough. The L and M beams are thus subjected tothe deflection field for a shorter period of time than they would be inthe absence of the shields 134 and 136. By properly relating thecumulative shielding lengths of the shields 134 and 136 to the relativebeam velocities and to the shape and length of the magnetic deflectionfield, the L and M beams are subjected to the deflection field forspecific time durations which will result in their being deflectedsubstantially the same amount as is the unshielded H beam.

By virtue of the spacing of the magnetic tube 142, from the end plate 63the M beam is dellected somewhat as it passes through the support 144.Because of this deflection, the M beam shield 136 must be made larger indiameter than the L beam shield 134 in order to prevent the deflected Mbeam from striking the shield elements. The M beam shield is made largerin diameter than the L beam shield for the further purpose ofsymmetrizing the field distortion which is caused by the shields 134 and136 and which the Unshielded H beam encounters.

Because of the magnetic tubular L and M beam shields, not only the sizesbut also the shapes of the three rasters are differentially affected. Inorder to adjust the aspect ratio of the H beam raster, a pair ofdeflection field enhancer elements 146 (FIGS. 1 and 4) of magneticmaterial are disposed on opposite sides of the H beam path. The pair ofenhancer elements 146 are attached to the end plate 63 -and extend alongthe H beam path in the deflection zone 20. The enhancer elements arepreferably tubular members having a rectangular cross section asillustrated. They are preferably disposed with their sides parallel tothe horizontal -and vertical directions of `deflection and with theiradjacent sides opposite each other. However, other cross sectionalshapes, such as U-shaped rectangular channel members, can be used.

A pair of enhancers disposed in both the horizontal and vertical fields,enhance the strength of the deilection field in one direction, e.g.,horizontal, and decrease the strength of the field in the perpendiculardirection, e.g., vertical, in the space between the enhancers which isthe region of the electron beam path with which they are associated. Itthe horizontal and vertical deflection fields are not coextensive andthe enhancers are disposed in only one of the fields, they affect onlythat field.

Since enhancers are placed adjacent a particular beam path and primarilyassociated therewith, they primarily affect the deilection field onlylocally for the particular beam associated therewith. Enhancers act asmagnetic conductors which are placed in the gap between a pair ofdellection coils and thus decrease the reluctance of the deflectionfield flux path in the localized area occupied by the enhancers.

The pair of H beam enhancers 146, being aligned in a horizontal plane,conduct the horizontally directed flux lines producing the vertical Hbeam deflection, thus enhancing the vertical deflection of the H beam,thereby to expand the H beam raster vertically.

In following the path of least reluctance, the horizontal flux lines ofthe vertical deflection field are bent toward aud pass through -theenhancers 146. The enhancers gather the flux lines from surroundingareas and concentrate them. Since the enhancers are arranged serially inthe direction of the flux lines, the flux in the 'area between :theenhancers 146 is concentrated and provides a stronger verticaldeilection field of the H beam than would otherwise exist without theenhancers. This serves to expand the height of the H beam raster. At thesame time, .the vertical flux lines of the horizontal deflection fieldare bent toward and pass through the enhancers 146. Since the enhancersare arranged in parallel in the direction of the horizontal deflectionflux lines, they gather flux which would otherwise pass -between theenhancers, and thereby the enhancers lower the flux concentration inthat area and provide a weaker horizontal deflection field for the Hbeam. This results in a horizontal contraction of the H beam raster. Thevertical expansion and horizontal contraction of the resulting H beamraster effect a change of the aspect ratio of the raster.

The electron -gun assembly 15 is preferably :angularly oriented aboutthe longitudinal axi-s of the tube S so as to produce la minimum ofobjectionable raster distortion. The Unshielded H beam is disposed inthe central plane which is perpendicular to the scan produced by thehigher frequency one of the two orthogonal deflection fields produced bythe yoke 118. According to present day practices in home televisionreceivers, the Unshielded H beam would be disposed in the centralvertical plane of the tube 8.

What is claimed is:

1. A cathode ray tube comprising:

(a) la luminescent screen, and

(b) la plurality of electron guns for projecting a plurality of electronbeams of different velocities toward said screen;

(c) each lof said guns including an electron beam electrostatic focuslens; the corresponding electrodes of said lenses -being electricallyconnected together;

(d) said focus lenses comprising means producing substantially equalimage distances for said plurality of different velocity beams.

2. A cathode ray tube comprising:

(a) a luminescent screen, and

(b) a plurality of electron guns for projecting different velocityelectron beams towards said screen;

(c) each of said guns including la unipotential lens system comprising apair of spaced anodes and a l l focus ring electrode surrounding at-least a portion of the gap between said anodes; the correspondingelectrodes of said lens ysystems being electrically connected together;

(d) the ratio of spacing between said anodes to the internal diameter ofsaid focus ring being different for each of said lens systems.

3. A cathode ray tube comprising:

(a) a luminescent screen, and

(b) a plurality of electron guns for projecting different velocityelectron beams towards said screen;

(c) each of said guns including a unipotential lens system comprising apair of spaced anodes and a focus ring electrode surrounding at least aportion of the gap between said anodes; the corresponding electrodes ofsaid lens `systems being electrically connected together;

(d) each of said focus ring electrodes of said lens systems having adifferent internal diameter.

4. A cathode r-ay tube comprising:

(a) `a luminescent screen, and

(b) a plurality of electron guns for projecting diierent velocityelectron beams towards said screen;

(c) each of said guns including a unipotential lens system comprisingapair of spaced anodes and `a focus ring electrode surrounding ,at leasta portion of the gap between said anodes; the corresponding elec-.trodes of lsaid lens systems 4being electrically connected together;

(d) each of said pair of anodes of each of said lens systems beingspaced :apart differently from the anodes of another of said lenssystems.

5. A cathode ray tube comprising:

(-a) a luminescent screen; and

(b) a plurality of electron guns for projecting a plurality of differentvelocity electron beams towards said screen;

(c) each of said guns including a dierent unipotential electrostaticlens system comprising a pair of spaced anodes and an intermediate focusring electrode;

(d) said plurality of focus ring electrodes being electrically connectedtogether;

(e) said plurality of anodes being electrically connected together;

(f) said lens systems comprising means producing substantially equallength image distances for said different velocity electron beams.

6. A cathode ray `tube comprising:

(a) a luminescent screen; and

(b) la plurality of electron guns each including a cathode electrode anda lirst accelerating anode electrode;

(c) said cathode electrodes being electrically separate and said anodeelectrodes being electrically connected together to permit the saidcathode and anode electrodes of each of said guns to be operated with a-voltage dierence therebetween which is different from the correspondingvoltage difference of the other of said guns to project diierentvelocity elec- 4tron beams toward said screen;

(d) said guns comprising means producing substantially equal gammas forsaid guns when so operated.

7. A cathode ray tube comprising:

(a) a luminescent screen; and

(b) a plurality of electron guns each including an assembly comprisingcathode, control, and anode electrodes next adjacent to each other inthe order named for projecting different velocity electron beams towardsaid screen; said cathodes yand control electrodes |being electricallyseparate and said anode electrodes being electrically connectedtogether;

(c) said guns comprising means producing equal transfer characteristicsof said guns when said assemblies are differentially energized toproject said different velocity beams.

8. A cathode ray tube as in claim 7 lwherein the spacing between thesaid cathode 'and t-he said anode of each of said guns is different fromthat of the other of said guns.

9. A cathode ray tube comprising:

(a) a luminescent screen; and

(b) a plurality of electron guns for projecting a plurality of diterentvelocity electron beams toward said screen;

(c) each of said guns including in the order named, a cathode, acontrol-electrode and a unipotential lens system comprising a pair ofspaced anodes and a focus ring electrode surrounding at least a portionof the gap between said anodes, the corresponding electrodes of saidlens systems being electrically connected together;

(d) the ratio of said spacing between said anodes to the aperturediameter of said focus ring electrode being different for each of saidguns;

(e) the control electrode and the nearest anode of each of said gunsbeing adjacent to each other without a screen electrode therebetween andcomprising means producing equal transfer characteristics of said gunswhen said guns are differentially energized to project said differentvelocity beams.

10. A cathode ray tube comprising:

(a) a luminescent screen; and

(b) a plurality of electron guns adapted to project a plurality ofdiierent velocity electron beams toward said screen;

(c) each of said guns including a cathode, a centrally aperturedcup-shaped control electrode, and a unipotential electrostatic lenssystem comprising a pair of spaced tubular anodes and a tubularfocussing ring electrode surrounding the gap between said anodes; thecorresponding electrodes of said lens systems being electricallyconnected together;

(d) said anodes of each of said guns being spaced apart a distancedifferent from the spacing between the anodes of the other of said guns.

11. A cathode ray tube comprising:

(a) a plurality of electron guns; and

(b) a luminescent screen including a plurality of layers of differentphosphors;

(c) each of said electron guns being adapted to project a diiferentvelocity electron beam toward said screen;

(d) each of said guns including a cathode, a control electrode and aunipotential electrostatic lens system comprising a pair of anodes and afocus ring electrode;

(e) the pair of anodes of each of said guns being spaced apart adistance different from the spacing of the anodes of the other guns;

(f) the cathodes of said guns being electrically separate with eachcathode having a separate lead-in conductor connected thereto forindividually energizing said cathodes with different voltages;

(g) the anodes of said guns being electrically interconnected and havinga lead-in conductor connected thereto for energizing said anodes with acommon voltage; and

(h) the focus ring electrodes of said guns being electricallyinterconnected and having a lead-in conductor connected thereto forenergizing said focus ring electrodes with a different common voltage.

12. A cathode ray tube comprising:

(a) an envelope;

(b) a plurality of lead-in conductors sealed through said envelope in apredetermined array;

(c) a high voltage terminal sealed through said envelope at a locationspaced from said array of lead-in conductors;

(d) a luminescent screen including a plurality of dilerent phosphorsdisposed on an internal surface of said envelope; and

(e) a plurality of electron guns each adapted to project a differentvelocity electron beam toward said screen;

(f) each of said guns including, in coaxial disposition, a cathode, acentrally apertured cup-shaped control electrode, and a unipotentialelectrostatic lens system comprising a pair of axially spaced tubularanodes and a tubular focus ring electrode surrounding the gap betweensaid anodes;

(g) the spacing between the pair of anodes of each of said electron gunsbeing different from that of the other of said guns;

(h) said cathodes being electrically separate from each other and eachof said cathodes being separately connected to different ones of saidlead-in conductors;

(i) said focus ring electrodes being electrically interconnected to eachother and to one of said lead-in conductors; and

(j) said anodes being electrically interconnected to each other and tosaid high voltage terminal.

13. A cathode ray tube comprising:

(a) a luminescent screen; and

(b) a plurality of electron guns for projecting different velocityelectron beams toward said screen;

(c) each of said guns including, in the order named, a cathode, acontrol electrode, and a unipotential electrostatic lens systemcomprising a first anode; said cathodes and said control electrodesbeing electrically separate and said first anodes being electricallyconnected together;

(d) said first anode of each gun being next adjacent the controlelectrode of the same gun and spaced therefrom a distance different fromthe spacing between the corresponding electrodes of the other guns.

14. A cathode ray tube comprising:

(a) a luminescent screen; and

(b) a plurality of electron guns for projecting a plurality of differentvelocity electron beams toward said screen;

(c) each of said guns including, in coaxial disposition in the ordernamed, a cath-ode, a control electrode, and a unipotential electrostaticlens system comprising a first anode, a focus ring electrode, and asecond anode; said cathodes and said control electrodes beingelectrically separate; the corresponding electrodes of said lens systemsbeing electrically connected together;

(d) said first anode of each gun being next adjacent the controlelectrode of the same gun;

(e) both the spacing between the control electrode and the first anodeand the spacing between the first and second anodes of each gun beingrespectively difierent from the corresponding spacings of the Votherguns.

15. A cathode ray tube comprising:

(a) a luminescentV screen; and

(b) a plurality of electron guns, each of which includes, in the ordernamed, a cathode', a control electrode, and a unipotential electrostaticlens system comprising a first anode, a focus ring electrode, `and asecond anode there being no electrode interposed between said firstanode and said control electrode of each gun; said cathodes and saidcontrol electrodes being electrically separate; the correspondingelectrodes of said lens systems being electrically connected together;

(c) the spacing between said anodes of each gun and the spacing betweensaid control electrode and said first anode of each gun being differentfrom the co1'- responding spacings of the other guns; and

(d) the electrode spacings of the guns being such that each gun whichhas a greater spacing between its anodes than does another of said gunsalso has a greater spacing between its first anode and control electrodethan does said another of said guns.

16. A cathode ray tube comprising:

(a) a luminescent screen;

(b) a plurality of electron guns adapted to project a plurality ofdifferent velocity electron beams toward said screen;

(c) each of said guns including, in coaxial relationship and in theorder named, a cathode, a centrally apertured cup-shaped controlelectrode, and a unipotential electrostatic lens system;

(d) each of said lens systems comprising axially spaced first and secondtubular anodes and a tubular focus ring electrode surrounding the gapbetween said anodes;

(e) the control electrode and first anode of each gun being nextadjacent to each other;

(f) first and second lead-in conductors;

(g) said focus ring electrodes being electrically interconnected to eachother and to said first lead-in conductor;

(h) said anodes being electrically interconnected to each other and tosaid second lead-in conductor; (i) and an additional plurality oflead-in conductors each separately connected to a different one o-f saidcathodes in each of said guns;

(j) both the spacing between the anodes and the spacing between thecontrol electrode and the first anode of each gun being different fromthe corresponding spacings of the other guns;

(k) the electrode spacings of the guns being such that each gun whichhas a greater spacing between its anodes than does another of said gunsalso has a greater spacing between its first anode and control electrodethan does said another of said guns.

17. A cathode ray tube comprising:

(a) a luminescent screen image surface; and

(b) a plurality of electron guns for projecting a plurality of differentVelocity electron beams toward said screen;

(c) each of said guns including a cathode electrode and a firstaccelerating electrode, which are next adjacent to each other withoutthe interposition therebetween of another electrode, said cathodeelectrodes being electrically separate and said accelerating electrodesbeing electrically connected together whereby the cathode electrode andaccelerating electrode of each gun are adapted to be operated with avoltage dif'- ference therebetween different from that of the others ofsaid guns, and a separate electron beam focus means;

(d) said guns comprising means producing substantially equal gammas whenso operated;

(e) said plurality of focus means comprising means producingsubstantially equal image distances for said different velocity electronbeams.

References Cited by the Examiner UNITED STATES PATENTS Messineo et al313-69 JAMES W. LAWRENCE, Primary Examiner.

Examiners.

C. R. CAMPBELL, P. C. DEMEO, Assistant Examiners.

Disclaimer 3,294,999.Fran3 ran Hekken, East Lampeter Township, LancasterCounty, Pn. CATHODE RAY TUBE. Patent dated Dec. 27, 1966. Disclaimerfiled Feh 1972, by the assigne, Radio orpomtz'o'n, of America. Herebj.`enten this disclaimer to claims 6 and 7 of said patent.

[01712-5112 Gazette November 14, 1.972.]

5. A CATHODE RAY TUBE COMPRISING: (A) A LUMINESCENT SCREEN; AND (B) APLURALITY OF ELECTRON GUNS FOR PROJECTING A PLURAILITY OF DIFFERENTVELOCITY ELECTRON BEAMS TOWARDS SAID SCREEN; (C) EACH OF SAID GUNSINCLUDING A DIFFERENT UNIPOTENTIAL ELECTROSTATIC LENS SYSTEM COMPRISINGA PAIR OF SPACED ANODES AND AN INTERMEDIATE FOCUS RING ELECTRODE; (D)SAID PLURALITY OF FOCUS RING ELECTRODES BEING ELECTRICALLY CONNECTEDTOGETHER; (E) SAID PLURALITY OF ANODES BEING ELECTRICALLY CONNECTEDTOGETHER; (F) SAID LENS SYSTEMS COMPRISING MEANS PRODUCING SUBSTANTIALLYEQUAL LENGTH IMAGE DISTANCES FOR SAID DIFFERENT VELOCITY ELECTRON BEAMS.